1. Field of the Invention
The invention relates to gas turbine engine turbine disk assemblies and, more particularly, to blade retainers or side plates used to axially retain blades mounted in slots in the disk and their seals to reduce cooling air from leaking into the hot turbine flowpath gas stream.
2. Description of Related Art
Gas turbine engines have a compressor and turbine which each include one or more annular rows of axially spaced fixed stator vanes which are positioned between rows of rotatable rotor blades. Each turbine blade has an airfoil portion, a platform portion and a root or dovetail portion which is mounted into a corresponding, axial slot formed in the rim of a turbine disk. The connection between the dovetail or root of the rotor blade and the axial slot in the disk rim prevents radial and tangential movement of each rotor blade relative to the disk.
Blade retainers, also referred to as side plates, are used to axially secure the turbine blades in the corresponding slots of the disk rim. The blade retainer also seals cooling air directed radially through disk and into the slots and through the blade shanks for cooling the turbine blades. Typically, the cooling air is compressor discharge pressure (CDP) air which has been routed around the combustor in order to internally cool high pressure turbine blades and vanes. The purpose of CDP air is to provide film cooling for airfoil surfaces directly in the path of these hot flowpath gases with maximum efficiency and minimum wastage of the cooling air potential since the turbine hardware is unable to withstand the hot gas temperature exiting the combustor without such protection. Lack of or improperly designed seals increase the cooling air requirements and allows the cooling air to enter the flowpath of the combustor gases.
Axial sealing between the blade retainer and the disk rim and blade roots to prevent blade cooling air from escaping the disk assembly is well known. Axial sealing, with or without wire annular seals for close clearances between the blade retainer, the blades and the disk rim have been found to allow cooling air losses because the sealing wire has imperfect contact with the blade and blade retainer. Other types of blade retainers such as shown in U.S. Pat. No. 4,890,981 issued to Corsmeier, et al., allowed the radial outer portion of the retainer to rest against the shank of the blade at an axial position without benefit of an additional sealing means at this point. Contact between the two materials existed during engine assembly; however, a small gap would form during engine operation due to different thermal gradients which would allow shank blade cooling air to escape into the aft blade cavity.